Declarative ObjectScript

Work with collections like a boss

Declarative ObjectScript - a proof-of-concept to show how to use declarative programming on ObjectScript.

Declarative programming - a style of building the structure and elements of computer programs—that expresses the logic of a computation without describing its control flow. (c) Wikipedia

Install with Docker

$ git clone https://github.com/atygaev/declarative-objectscript
$ cd declarative-objectscript
$ docker-compose up -d
$ docker-compose exec iris iris session iris

USER> zn "IRISAPP"

Run Demo

What about to find even numbers in given collection of numbers [1, 2, 3, 4]?

IRISAPP> // run legacy code
IRISAPP> do ##class(Demo.App).RunWithLegacyCode()
Even numbers: 2, 4

Source of RunWithLegacyCode

IRISAPP> // run DeclarativeOS code
IRISAPP> do ##class(Demo.App).RunWithDeclarativeOS()
Even numbers: 2, 4

Source of RunWithDeclarativeOS

Just compare two variants: RunWithDeclarativeOS and RunWithLegacyCode. Both does the same, but there is a difference…

 Class Demo.App Extends DeclarativeOS.RegistryHelper 
 { 
 /// @Declarative("examples:isEven") 
 ClassMethod IsEven(number As %Numeric) As %Boolean 
 { 
     return number # 2 = 0 
 } 
 
 ClassMethod RunWithDeclarativeOS() 
 { 
     set numbers = ##class(%ListOfDataTypes).%New() 
     for i=1:1:4 { do numbers.Insert(i) } 

     set evenNumbers = $zfilter(numbers, "examples:isEven") // sexy and short

     write "Even numbers: " _ $zjoin(evenNumbers, " ") // printing collection
 } 
 
 ClassMethod RunWithLegacyCode() 
 { 
     set numbers = ##class(%ListOfDataTypes).%New() 
     for i=1:1:4 { do numbers.Insert(i) } 

     set evenNumbers = ##class(%ListOfDataTypes).%New() // iterate explicitly
     set index = "" 
     for { 
         set index = numbers.Next(index) // working with indexes
         quit:index="" 
         set item = numbers.GetAt(index) 
         if (item # 2 = 0) { 
             do evenNumbers.Insert(item) 
         } 
     } 

     write "Even numbers: " 
     for i=1:1:evenNumbers.Count() { write evenNumbers.GetAt(i) _ " " } // printing collection
 } 
 }

Content

• Installation
  • Use ZPM
  • Use Docker
  • Use XML
• Examples
  • Iterate (zforeach)
  • Join ($zjoin)
  • Filter ($zfilter)
  • Find ($zfind)
  • Exist ($zexists)
  • Count ($zcount)
• How It works
• License (MIT)

Installation

Use ZPM

You can install the DeclarativeOS by using ZPM

ZPM: USER>install declarative-os

Use Docker

$ git clone https://github.com/atygaev/declarative-objectscript
$ cd declarative-objectscript
$ docker-compose up -d
$ docker-compose exec iris iris session iris

Use XML

Download the install.declarative-os.xml from latest release.

https://github.com/atygaev/declarative-objectscript/releases/download/v1.0.2/install.declarative-os.xml

Install the project via terminal:

USER> set installFile = "<path to downloaded install.declarative-os.xml>"
USER> do $system.OBJ.Load(installFile)

Examples

Let me show some examples.

Iterate

Applies given action to every item in collection.

USER> set words = ##class(%ListOfDataTypes).%New()
USER> do words.Insert("Hello ")
USER> do words.Insert("World!")
USER>
USER> // Output collection
USER> zforeach $zbind(words, "io:print")

Hello world!

Join

Joins collection items to a string by using given separator.

USER> set words = ##class(%ListOfDataTypes).%New()
USER> do words.Insert("Tic")
USER> do words.Insert("Tac")
USER> do words.Insert("Toe")
USER>
USER> // Concat words by using "-"
USER> write $zjoin(words, "-")

Tic-Tac-Toe

Filter

Returns new collection with filtered items only.

USER> set numbers = ##class(%ListOfDataTypes).%New()
USER> do numbers.Insert(1)
USER> do numbers.Insert(2)
USER> do numbers.Insert(3)
USER> do numbers.Insert(4)
USER>
USER> // Filter collection to find even numbers
USER> set evenNumbers = $zfilter(numbers, "examples:isEven")
USER>
USER> // Output even numbers
USER> write "Even numbers: " _ $zjoin(evenNumbers, ", "), !

Even numbers: 2, 4

Find

Finds first item which satisfies given criteria.

USER> set numbers = ##class(%ListOfDataTypes).%New()
USER> do numbers.Insert(4)
USER> do numbers.Insert(5)
USER> do numbers.Insert(6)
USER>
USER> // Find prime number
USER> set primeNumber = $zfind(numbers, "examples:isPrime")
USER>
USER> write "Prime number: " _ primeNumber

Prime number: 5

Exists

Returns $$$YES if collection contains at least one item which satisfies the given criteria.

Otherwise, returns $$$NO.

USER> set numbers = ##class(%ListOfDataTypes).%New()
USER> do numbers.Insert(13)
USER> do numbers.Insert(12)
USER> do numbers.Insert(11)
USER> do numbers.Insert(10)
USER>
USER> // Check whether collection contains at least one palindromic number.
USER> set hasPalindromicNumbers = $zexists(numbers, "examples:isPalindromic")
USER>
USER> write "Collection has palindromic numbers? " _ $case(hasPalindromicNumbers, 1:"YES", 0:"NO")

Collection has palindromic numbers? YES

Count

Counts items which satisfy the given criteria.

USER> set numbers = ##class(%ListOfDataTypes).%New()
USER> do numbers.Insert(2)
USER> do numbers.Insert(3)
USER> do numbers.Insert(4)
USER> do numbers.Insert(5)
USER>
USER> // Counts prime numbers in given collection of numbers.
USER> set primeNumbersCount = $zcount(numbers, "examples:isPrime")
USER>
USER> write "Count of prime numbers: " _ primeNumbersCount

Count of prime numbers: 3

How it works

In two words: call $classmethod.

But $classmethod requires class name and method name.

And it looks really long and weird. So I invented aliases.

Alias is a string identifier for pair of Class and ClassMethod.

USER> // instead of this
USER> set evenNumbers = $zmap(numbers, "Test.DeclarativeOS.MathDeclaratives", "isEven")
USER>
USER> // using alias
USER> set evenNumbers = $zmap(numbers, "math:isEven")

How define own declaratives

You can define your own declaratives.

Just follow 3 steps:

• Extend from DeclarativeOS.RegistryHelper;
• Implement class method;
• Mark the method.

Step 1. Extends from DeclarativeOS.RegistryHelper

Class Demo.MathDeclaratives extens DeclarativeOS.RegistryHelper
{
}

Step 2. Implement class method

Class Demo.MathDeclaratives extens DeclarativeOS.RegistryHelper
{

ClassMethod sqrt(value As %Numeric)
{
    return $zsqr(value)
}

ClassMethod square(value As %Numeric)
{
    return $zpower(value, 2)
}

}

Step 3. Mark the method

Class Demo.MathDeclaratives extens DeclarativeOS.RegistryHelper
{

/// @Declarative("math:sqrt")
ClassMethod sqrt(value As %Numeric)
{
    return $zsqr(value)
}

/// @Declarative("math:square")
ClassMethod square(value As %Numeric)
{
    return $zpower(value, 2)
}

}

Step 4. Try it

s numbers = ##class(%ListOfDataTypes).%New()
d numbers.Insert(4)
d numbers.Insert(9)

w "Sqrt every number: " _ $zjoin($zmap(numbers, "math:sqrt"), ", "), !
w "Square every number: " _ $zjoin($zmap(numbers, "math:square"), ", "), !

Sqrt every number: 2 3
Square every number: 16 81

Contribution

Any contribution is really welcome.

MIT License

Copyright (c) 2017 InterSystems Developer Community

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.